CVE-2021-46939 tracing: Restructure trace_clock_global() to never block

2024-02-2718:40:27

Linux

www.cve.org

linux kernel

vulnerability

fix

tracing

deadlock

restructure

bugzilla

cve-2021-46939

6.1 Medium

AI Score

Confidence

High

0.0004 Low

EPSS

Percentile

5.1%

JSON

In the Linux kernel, the following vulnerability has been resolved:

tracing: Restructure trace_clock_global() to never block

It was reported that a fix to the ring buffer recursion detection would
cause a hung machine when performing suspend / resume testing. The
following backtrace was extracted from debugging that case:

Call Trace:
trace_clock_global+0x91/0xa0
__rb_reserve_next+0x237/0x460
ring_buffer_lock_reserve+0x12a/0x3f0
trace_buffer_lock_reserve+0x10/0x50
__trace_graph_return+0x1f/0x80
trace_graph_return+0xb7/0xf0
? trace_clock_global+0x91/0xa0
ftrace_return_to_handler+0x8b/0xf0
? pv_hash+0xa0/0xa0
return_to_handler+0x15/0x30
? ftrace_graph_caller+0xa0/0xa0
? trace_clock_global+0x91/0xa0
? __rb_reserve_next+0x237/0x460
? ring_buffer_lock_reserve+0x12a/0x3f0
? trace_event_buffer_lock_reserve+0x3c/0x120
? trace_event_buffer_reserve+0x6b/0xc0
? trace_event_raw_event_device_pm_callback_start+0x125/0x2d0
? dpm_run_callback+0x3b/0xc0
? pm_ops_is_empty+0x50/0x50
? platform_get_irq_byname_optional+0x90/0x90
? trace_device_pm_callback_start+0x82/0xd0
? dpm_run_callback+0x49/0xc0

With the following RIP:

RIP: 0010:native_queued_spin_lock_slowpath+0x69/0x200

Since the fix to the recursion detection would allow a single recursion to
happen while tracing, this lead to the trace_clock_global() taking a spin
lock and then trying to take it again:

ring_buffer_lock_reserve() {
trace_clock_global() {
arch_spin_lock() {
queued_spin_lock_slowpath() {
/* lock taken /
(something else gets traced by function graph tracer)
ring_buffer_lock_reserve() {
trace_clock_global() {
arch_spin_lock() {
queued_spin_lock_slowpath() {
/ DEAD LOCK! */

Tracing should never block, as it can lead to strange lockups like the
above.

Restructure the trace_clock_global() code to instead of simply taking a
lock to update the recorded “prev_time” simply use it, as two events
happening on two different CPUs that calls this at the same time, really
doesn’t matter which one goes first. Use a trylock to grab the lock for
updating the prev_time, and if it fails, simply try again the next time.
If it failed to be taken, that means something else is already updating
it.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=212761

CNA Affected

[
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "unaffected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "kernel/trace/trace_clock.c"
    ],
    "versions": [
      {
        "version": "14131f2f98ac",
        "lessThan": "91ca6f6a91f6",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "14131f2f98ac",
        "lessThan": "859b47a43f5a",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "14131f2f98ac",
        "lessThan": "1fca00920327",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "14131f2f98ac",
        "lessThan": "d43d56dbf452",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "14131f2f98ac",
        "lessThan": "c64da3294a7d",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "14131f2f98ac",
        "lessThan": "a33614d52e97",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "14131f2f98ac",
        "lessThan": "6e2418576228",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "14131f2f98ac",
        "lessThan": "2a1bd74b8186",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "14131f2f98ac",
        "lessThan": "aafe104aa909",
        "status": "affected",
        "versionType": "git"
      }
    ]
  },
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "affected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "kernel/trace/trace_clock.c"
    ],
    "versions": [
      {
        "version": "2.6.30",
        "status": "affected"
      },
      {
        "version": "0",
        "lessThan": "2.6.30",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "4.4.269",
        "lessThanOrEqual": "4.4.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "4.9.269",
        "lessThanOrEqual": "4.9.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "4.14.233",
        "lessThanOrEqual": "4.14.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "4.19.191",
        "lessThanOrEqual": "4.19.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.4.118",
        "lessThanOrEqual": "5.4.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.10.36",
        "lessThanOrEqual": "5.10.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.11.20",
        "lessThanOrEqual": "5.11.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.12.3",
        "lessThanOrEqual": "5.12.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.13",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]